(1) Field of the Invention
The invention relates to an articulated unit for a motor vehicle with a housing and a link pin supported in the housing and a bearing shell disposed between the housing and a bearing section of the link pin, with the bearing shell supported with its outer surface at least in sections in the housing and having on its inner surface facing the bearing section of the link pin recesses for a lubricant, and a method for lubricating an articulated unit.
(2) Description of Related Art
DE 44 19 954 A1 discloses an articulated unit of the aforedescribed type for a motor vehicle, wherein the articulated unit described in the publication shows a ball joint for a motor vehicle. This ball joint has a housing and a link pin supported in the housing, as well as a bearing shell disposed between the housing and the bearing section of the link pin, wherein the bearing shell is supported with its outer surface, at least in sections, in the housing. The bearing shell has recesses for a lubricant, so-called “lubricant grooves,” on the inner surface facing the bearing section of the link pin which is formed as an articulated ball. The recesses disclosed in the document are implemented as lubricant grooves with a groove structure and are intended to distribute the lubricant in the articulated unit so as to optimize the sliding friction between the bearing section of the link pin and the bearing shell. The groove-shaped recesses disposed in the inner surface of the bearing shell create a kind of lubricant reservoir.
Compared to conventional ball joints, articulated units of the type the described in DE 44 19 954 A1 exhibit under normal operating conditions significant advantages in lubricating the components moving relative to one another. However, it has been observed that in particular for smaller, high-frequency movements of the link pin within the housing, the lubricant disposed in the bearing shell is pressed out of the support region of the bearing shell, thereby creating dry friction which is formed at least partially between the bearing section of the link pin and the bearing shell. In this embodiment, the lubricant in the articulated unit escapes through a vent bore located in the center of the bearing shell into a cavity present in the housing. However, the lubricant in this cavity is then no longer available for the components of the articulated unit that move relative to one another, because there is no return path for the lubricant to the region of the surfaces that need to be lubricated, so that lubrication is no longer possible.
An extended idle time also poses a problem for articulated units, because a high initial breakaway torque is then formed, because of due to the lack of joint movement, the lubricant disposed between the bearing section of the link pin and the inner surface of the bearing shell is pressed out of the contact region.